Development dynamic compartment models to predict behavior of radionuclides in rice paddy field Tomoyuki TAKAHASHI Kyoto University Research Reactor Institute Osaka, Japan

My main experiences on development of dynamic compartment models BIOMOVS II uranium mill tailings scenario (U-238 chain) with Dr. Homma and Dr. Togawa (JAEA) Transfer of tritium by river network at Toki site with Dr. Yamanishi (NIFS) Dr. Momoshima and Dr. Sugihara (Kyushu Univ.) Behavior of radionuclides in rice paddy field - Iodine, Cesium and Strontium - Carbon-14 (EMRAS I) with Dr. Uchida, Dr. Tagami, Dr. Ishii and Dr. Takeda (NIRS) Dr. Yamamoto (Y first Inc.) Dr. Tomita and Dr. Hayashi (V.I.C. Inc.)

BIOMOVS II uranium mill tailings scenario (U-238 chain) Source term: - Groundwater release (leaching from tailings pile) - Atmospheric release (dust and gas from tailings pile) Dynamic compartment: Vegetable land and pasture land Deterministic analysis -Time dependent annual total dose (each nuclides and total) Probabilistic analysis - Cumulative distribution functions of peak total dose - Time dependent 90% confidence interval - Statistical coefficients between variable parameters and peak total dose

River and sampling points of river waters in Toki area Meeting point

Network of rivers assumed in the analysis Basin Toki river C-2 B-1 B-1 C-1 Basin B-3 Basin F-3 F-1 A-2 A-1 F-2 A-3 Ikuta river Tsumaki river Downstream

Compartment models for basin and meeting point (a) Basin Rainfall Evaporation River water of downstream River water Surface flow Groundwater Infiltration A migration prediction code "MOGRA" was used (b) Meeting point River water of upstream River water of downstream River water River water of upstream

Measured and estimated tritium concentration in river water and groundwater Estimated concentration in groundwater at B-1 point Estimated concentration in river water at B-1 point Measured concentration in groundwater Measured concentration at B-2 point Measured concentration at B-1 point Measured concentration at B-3 point

Behavior of radionuclides in rice paddy field Background and objectives Reasonable dose assessment caused by nuclear facilities Appropriate estimation of internal dose by the pathway of ingestion of rice which is a staple food in Asian countries Prediction of behavior of radionuclides in rice paddy field Development of dynamic compartment models for some important radionuclides

Structure of compartment model for I, Cs and Sr Air Rain Harvest Outside Deposition Ear Hull Bran Rice Plowing Translocation Translocation Leaf & stem Leaf & stem surface Leaf & stem internal Leaf & stem through Outside Weathering Root uptake Water Volatilization 　　　　　　　　　　　　Surface water　　　　　　　　　　　 Outflow Outside Irrigation Sorption & desorption Sorption & desorption Change Soil (fast) Soil (slow) Plowing Deeper zone Infiltration Infiltration

Growing curve of rice plant Ishizuka & Tanaka (1953) Total Leaf & stem WTotal WLeaf =WTotal-WEar Estimated parameters Ear K(d-1) T1/2(d) Wmax(g) Total 0.06 54 12.3 Ear 0.09 66 7.1 WEar Leaf & stem = Total - Ear Growing curve

Development of a Dynamic Compartment Model for Prediction of Transfer of Carbon-14 to Rice Grains 14C is one of the most critical radionuclide for the safety assessment - Nuclear fuel reprocessing plant - Radioactive waste disposal plant Developed a dynamic compartment model to predict 14C behavior in rice paddy field and its concentration in rice grains First step The source term was considered as 14CO2 released into the atmosphere Second step The source term was considered as 14C with the irrigation water

Structure of compartment model for 14C from the atmosphere Inflow Respiration Air Leaf & stem organic Ear organic Translocation Respiration Photosynthesis Photosynthesis Absorption Plant inorganic Exchange Uptake Release Translocation Revise to more appropriate parameter values Soil Translocation Outflow

Scheme of compartment model for 14C from the irrigation water Respiration Air nearby rice plant Respiration Leaf & stem organic Ear organic Translocation Photosynthesis Photosynthesis Absorption Plant inorganic Exchange Source Sink Root uptake Irrigation Outflow Exchange Uptake Irrigated water Release Volatilization Exchange Exchange Exchange Exchange Soil 1 Soil 2 Mixture Infiltration Infiltration Mixture Outside Air Sink

Scheme of compartment model for 14C from the irrigation water Respiration Air nearby rice plant Respiration Leaf & stem organic Ear organic Estimation of parameter values from batch experiment with Dr. Uchida, Dr. Tagami, Dr. Ishii and Dr. Yamamoto Translocation Photosynthesis Photosynthesis Absorption Plant inorganic Exchange Source Sink Root uptake Irrigation Outflow Important pathway Exchange Uptake Irrigated water Release Volatilization Exchange Exchange Exchange Exchange Soil 1 Soil 2 Mixture Infiltration Infiltration Outside Sink

Estimation of transfer parameters between soil, water and air Gas Water Soil Soil/water Distribution in each phase (%) Conc. in soil / Conc. in water (mL/g) days